The Evap Canister is located in the fender well, if I am not mistaken and the B1S2 is the O2 sensor is the second O2 sensor on the left side of the engine if your looking at it from the front of the motor.

Yes there are 4 sensors, one on each bank of your V6 above the catalytic converter and also a pair below the cats, maybe you should find an independent garage to put the Mazda on their code reader and find out the whole picture, my reader cost $300 and is low end but gives all the info on each O2 sensor (and all other sensors) in real time so I can see how many are going off spec and need changing. Dealerships work to manufacturers reccomendations and guidelines so probably have to change the pair.

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Some manufacturers use a kind of shorthand that reads different, but means the same thing:
Sensor 1/1 or O2s 1/1
Sensor 2/1 or O2s 2/1
Sensor 1/2 or O2s 1/2
Sensor 2/2 or O2s 2/2

Bank 1 is always the side of the engine where cylinder number 1 is located and, of coarse, Bank 2 is the opposite side.
On a 4 cylinder engine, there is only 1 bank and it is always referred to as Bank 1.

Sensor 1 is always the upstream sensor (the one located BEFORE the catalytic converter)
Sensor 2 is always the downstream sensor (the one that is located AFTER the catalytic converter.

Some manufacturers use a kind of shorthand that reads different, but means the same thing:
Sensor 1/1 or O2s 1/1
Sensor 2/1 or O2s 2/1
Sensor 1/2 or O2s 1/2
Sensor 2/2 or O2s 2/2

Bank 1 is always the side of the engine where cylinder number 1 is located and, of coarse, Bank 2 is the opposite side.
On a 4 cylinder engine, there is only 1 bank and it is always referred to as Bank 1.

Sensor 1 is always the upstream sensor (The one located BEFORE the catalytic converter)
Sensor 2 is always the downstream sensor (the one that is located AFTER the catalytic converter.

A code P0155 may mean that one or more of the following has happened: * O2 Heater element resistance is high * Internal short or open in the heater element * O2 heater circuit wiring high resistance * open or short to ground in the wiring harness

Possible Solutions: * Repair short or open or high resistance in wiring harness or harness connectors * Replace oxygen sensor (cannot repair open or short that occurs internally to sensor)

Some manufacturers use a kind of shorthand that reads different, but means the same thing:
Sensor 1/1 or O2s 1/1
Sensor 2/1 or O2s 2/1
Sensor 1/2 or O2s 1/2
Sensor 2/2 or O2s 2/2

Bank 1 is always the side of the engine where cylinder number 1 is located and, of coarse, Bank 2 is the opposite side.
On a 4 cylinder engine, there is only 1 bank and it is always referred to as Bank 1.

Sensor 1 is always the upstream sensor (The one located BEFORE the catalytic converter)
Sensor 2 is always the downstream sensor (the one that is located AFTER the catalytic converter.

bank 1 is the drivers side bank, so b1s1 would be the drivers side closest to the engine. if the truck is equipped with several 02 sensors then bank 2 or b2s1 would be passenger side closest to the engine. those are called upstream o2 sensors and the others downstream b1s2 and b1s2 b= bank 1= drivers side s=sensor 2=downstream. hope this helps.

First of all if it is a 6 cylinder its an inline engine (4.0L). The reason I bring this up is it changes your O2 sensor configuration. Bank 1 sensor 1 ( there is only one bank because only 1 manifold) is the primary O2 sensor controlling the air/fuel ratio dependant on other sensors. Bank 1 sensor 2 is After the cataylistic converter. Depending on the code if low input or high input could be wiring and not a sensor at all. Also a low flow or high flow could indicate somebody previously "punched" the converter out or it is getting clogged due to age and mileage. Hope this helps.